Recent developments in the analysis of liquids emphasize automation and the use of so-called "micro-methods". However, the automation of liquid analysis techniques using very small quantities of liquid, i.e., quantities of the order magnitude of a few microliters, has been limited because of difficulities in measuring out these small quantities with high reproducibility.
The limitations on these dosing techniques can be traced largely to the valves used in the dosing devices. Most of the valves in dosing devices of this type utilize a valve body in the form of a cone or ball which seals against a corresponding valve seat under forces generated by gravity, hydraulic pressure or mechanical biassing devices such as springs. The reproducibility afforded by the devices is poor for small quantities of liquid because of factors such as friction, leakage, wear and the strong resistance to opening provided by some of the valves of this type.